1. Field of the Invention
The present invention relates generally to a torque control device for a vibration dampening and shock absorbing apparatus for a blast hole drilling machine, and more specifically, to a torque control device for absorbing axial and torsional forces during the operation of a rotary drilling machine.
2. Background of the Invention
In various types of drilling operations, the drill bit is forced downward under pressure while being rotated in order to penetrate earthen formations. These drilling operations can require the application of relatively high downward force to the drill bit as well as relatively high torque to turn the drill bit.
One example is the typical rotary blast hole drill which comprises a large drilling rig to which is attached a rotary drive mechanism. Typically, the drill's rotary drive is capable of being raised and lowered along a substantially vertical axis directly above the formation to be drilled. Additionally, a length of drill pipe or drill string is connected to the rotary drive so as to extend downwardly therefrom in a substantially vertical direction. A drill bit is secured to the downward end of the drill pipe. The drill machine's rotary drive head is activated to rotate both the drill pipe and the drill bit at the desired speed. Then, the rotary drive, together with the drill pipe and bit, is lowered so that the drill bit contacts the surface of the formation to be drilled. Downward pressure is then continuously applied to the rotating drill pipe and bit to force the drill bit to cut downwardly into the formation. As the drilling operation occurs, air is forced through the interior of the drive head, drill pipe, and through the drill bit, thereby forcing cuttings out of the hole and maintaining a clear surface upon which the drill bit may operate.
When the drilled hole is deep enough to accommodate the first length of drill pipe, the drill's rotary drive is disconnected from the drill pipe and raised to its original position. A second length of drill pipe is then connected between the rotary drive and the first length of drill pipe, The rotary drive is then activated and drilling operations are continued. This procedure is repeated until a desired hole depth is achieved.
In order to eliminate the problems associated with vibration and shock to the drilling apparatus, various devices have been employed to dampen vibrations and absorb torsional forces during the operation of the rotary drill. These devices typically comprise a force absorbing apparatus which is connected between the drill machine's rotary drive head and the drill pipe. In some instances, the force absorbing device includes some type of resilient material which absorbs the vibrations and shocks, thereby dissipating the undesirable energy associated with the drilling operation.
U.S. Pat. Nos. 3,746,330 and 3,947,009 show a resilient coupling provided between a drive shaft and a driven shaft of a tubular drill string in a rotary drilling machine. A group of resilient discs are sandwiched between a series of axially-spaced drive, driven and pressure plates which surround drive and driven shaft members. Pin projections extend from the driven plate into the resilient discs while fastening means extend between the drive and pressure plates for compressing the resilient discs together and into union with the pin projections and fastening means.
U.S. Pat. No. 4,109,488 shows a shock absorbing rotary drive coupling for a rotary blast hole drill. The device includes two parallel, horizontal plates. One of the plates, the drive plate, is connected to the rotary drive and the other, the driven plate, is connected to the driven shaft, or drill pipe. The apparatus further includes a resilient member which is bonded between the two plates. The entire apparatus has a hole through its center in order to accommodate the air and fluid which is forced through the drill pipe to the drill bit. Additionally, it has been known in the art to fasten nylon straps to the respective plates. The resilient pad twists and the straps tighten when a predetermined amount of torque is applied to the driven plate. The torque generated by the drive plate is then transferred directly to the driven plate by nylon straps, causing the drive plate to directly drive the driven plate and relieve the torque on the resilient pad. A problem with the nylon straps is that they frequently tear or stretch and, therefore, do not always adequately protect the resilient pad. In addition, the nylon strap can be torn or stretched in a lifting situation, which limits their longevity.